Diagnostic role and clinical correlates of anti-Saccharomyces cerevisiae antibodies (ASCA) and anti-neutrophil cytoplasmic antibodies (p-ANCA) in Italian patients with inflammatory bowel diseases.

BACKGROUND: Anti-Saccharomyces cerevisiae antibodies (ASCA) and perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) are serological markers associated, respectively, with Crohn's disease and ulcerative colitis, whose clinical significance and possible diagnostic role are still poorly defined. AIMS: (a) To evaluate the sensitivity, specificity and predictive values of isolated and combined ASCA and p-ANCA assays in a large cohort of Italian patients with inflammatory bowel disease (IBD) and (b) to assess whether their presence is associated with particular clinical features of the disease. PATIENTS AND METHODS: Hundred and forty-six IBD patients (93 with Crohn's disease and 53 with ulcerative colitis) and 54 control patients were enrolled in the study. ASCA (IgA and IgG) and p-ANCA were determined by means of enzyme-linked immunosorbent assay and indirect immunofluorescence, respectively.
RESULTS: The specificities were excellent for both tests (ASCA in Crohn's disease, 98.1% both for IgA and IgG, and p-ANCA in ulcerative colitis, 92.5%); however, the sensitivities of both tests were low (59.1% for ASCA IgA, 44.1% for ASCA IgG, 39.6% for p-ANCA). ASCA specificity and positive predictive value reached 100% when positivity for both IgA and IgG was present. No significant association was found between the presence of a specific serological marker and patients' clinical features.
CONCLUSIONS: This study confirms the low prevalence of p-ANCA observed in ulcerative colitis patients from the Mediterranean area. The low sensitivity of ASCA and p-ANCA, despite their rather high specificity, renders them of little value in the screening of the general population, where the prevalence of IBD is low. However, in our series, a double positivity for ASCA IgA and IgG identifies with certainty the presence of Crohn's disease.